Abstract: Dentritic cells（DCs）and their progenitors from murine bone marrow were collected and induced in vitro by both granulocyte-macrophage colony-stimulating （GM-CSF） and interleukin-4 （11,4） for 5?6 days. Immature DCs were loaded with apoptotic tumor cells （AP-DC），then AP-DC vaccines were induced further maturation stimulated with MCD40L-CHO cells and TNF-arespectively for 48 h. These DCs’ morphology was observed under transmission electron micro-scropy. We found that immature DCs showed a few short and blunt cytoplasmic processes,there were specific morphology granules which liked earphone in some cells；the immature DCs had a powerful ability to capture antigens from apoptotic tumor cells in 5-6 th culturing day，the DCs engulfing the apoptotic bodies were observed； sub-cellular structures between CD40 ligation and TNF-astimulated DCs were different, the former had typical morphology of DCs which exhibited many dendritic protrusions and the nucleus was irregular in shape，the cytoplasm contained numerous mitochondria, ribosomes，well-developed Golgi complexes, but scantly lysosomes. In addition,DCs might be in contact with each other. The results suggested that DCs were heterogeneous；DCs can acquire antigen by phagocytosing apoptotic bodies ；CD40 ligation and the associated signal transduction played an essential role in myeloid DCs differentiation and maturation.

Key words: Dendritic cells, Ultrastructure, CD40, Loading antigen